A reinforced soil structure combines a compacted fill, a facing and reinforcements usually connected to the facing.
Various types of reinforcement can be used: metal (for example galvanized steel), synthetic (for example based on polyester fibers), etc. They are placed in the earth with a density that is dependent on the stresses that might be exerted on the structure, the thrust of the soil being reacted by the friction between the earth and the reinforcements.
The facing is usually made from prefabricated concrete elements, in the form of panels or blocks, juxtaposed to cover the front face of the structure.
There may be horizontal steps on this front face between various levels of the facing, when the structure incorporates one or more terraces. In certain structures, the facing may be built in situ by pouring concrete or a special cement.
The reinforcements placed in the fill are secured to the facing by mechanical connecting members that may take various forms. Once the structure is completed, the reinforcements distributed through the fill transmit high loads, that may range up to several tons. Their connection to the facing needs therefore to be robust in order to maintain the cohesion of the whole.
These connections between the reinforcements entail a risk that the maximum load they can withstand may be exceeded if the soil undergoes differential settlement or in the event of an earthquake. Furthermore, the connecting members exhibit risks of degradation. They are often sensitive to corrosion due to moisture or chemical agents present in or which have infiltrated into the fill. This disadvantage often prevents the use of metal connecting members. The connecting members are sometimes based on resins or composite materials so that they degrade less readily. However, their cost is then higher, and it is difficult to give them good mechanical properties without resorting to metal parts. For example, if the reinforcements are in the form of flexible strips and attach by forming a loop behind a bar secured to the facing (U.S. Pat. No. 4,343,571, EP-A-1 114 896), such bar undergoes bending stresses, which is not ideal in the case of synthetic materials.
By construction, the prefabricated facing elements have a determined number of locations for connection to the reinforcements of the fill. This results in constraints on the overall design of the structure, particularly in terms of the density with which the reinforcements can be placed. For example, if the prefabricated elements each offer four attachment points, the designer will need to envisage connecting the reinforcements there that many times, or possibly a lower number of times, the number always being a whole number. If structural engineering considerations require, for example, 2.5 pairs of main reinforcements per prefabricated element, it is necessary to provide a substantial surplus of reinforcements, which has an significant impact on the cost. These considerations complicate the design of the structure, since the optimization generally requires reinforcement densities that can vary from one point in the fill to another.